Recently, in Fong, et al, U.S. Pat. No. 4,022,950, the observation of Chl a photogalvanic water splitting reactions that result from irradiation of the chlorphyll a dihydrate aggregate (Chl a.sup.. 2H.sub.2 O).sub.n in the far red wavelength region was disclosed. However, the quantum efficiency of the observed effects was low, and we were unable to detect the discharge of H.sub.2 by direct analytical means. The photoelectrolysis of water is a direct process for harvesting solar energy to produce gaseous hydrogen for fuel. Considerable attention has been focused on n-type semiconducting photoanodes such as TiO.sub.2 and SrTiO.sub.3. However, these materials operate in the near ultraviolet wavelength region where the solar radiant energy density is low.
In our earlier photochemical conversion experiments, as reported in J. Amer. Chem. Soc., Vol 99, p. 5802 (1977), the chlorophyll a was plated on a shiny Pt electrode. The photolytic reactions were detected by measuring the flow of electrons in an external circuit of a photogalvanic assembly consisting of a Pt-Chl suspended electrode suspended in an aqueous electrolyte in a half cell and a Chl a-free electrode suspended in another half cell. That apparatus, while novel, provided only a low quantum efficiency.